Sensor device and method for manufacture

ABSTRACT

A sensor device has a ceramic carrier substrate. At least two conductor tracks are arranged on the carrier substrate. The sensor device has at least one ceramic component that is in the form of a chip and is connected to the conductor tracks in an electrically conductive manner. The at least one ceramic component is mechanically connected to the conductor tracks by means of a screen printing paste which has been burnt in.

This application is a continuation of co-pending InternationalApplication No. PCT/EP2009/060306, filed Aug. 7, 2009, which designatedthe United States and was not published in English, and which claimspriority to German Application No. 10 2008 036 837.7, filed Aug. 7,2008, both of which applications are incorporated herein by reference.

BACKGROUND

The German publication 10 2006 031 344 A1 discloses a sensor arrangementin which a sensor element is arranged in a plate arrangement.

SUMMARY

In one aspect a sensor device has a simple and stable structure.

A sensor device comprises a ceramic carrier, where at least twoconductor tracks are arranged on the carrier substrate. The sensordevice has at least one ceramic component that is in the form of a chipand is connected to the conductor tracks of the ceramic carriersubstrate in an electrically conductive manner.

The ceramic component preferably comprises a temperature-dependentresistance which can be used to convert a detected physical variableinto an electrical signal.

The following features of the ceramic component are described, by way ofexample, for one or more NTC elements.

However, the following features also apply to any other desired ceramiccomponent which is suitable for converting a physical variable into anelectrical measurement signal.

The ceramic component is preferably in the form of atemperature-resistant temperature sensor. In one advantageousembodiment, the ceramic component is in the form of an NTC element andcomprises a body containing NTC ceramic. In this case, NTC stands forNegative Temperature Coefficient. The NTC element is preferably in theform of an unpackaged ceramic chip. The NTC ceramic is preferablyresistant to aging. The NTC ceramic preferably has a high degree ofsensitivity with respect to a temperature measurement. The NTC ceramiccomprises, for example, a manganese/nickel ceramic which preferably hasa spinal structure.

The at least one NTC element is connected to the conductor tracks of theceramic carrier substrate of the sensor device in a mechanically fixedmanner by means of a screen printing paste which has been burnt in. Amechanical connection between the NTC element and the carrier substrateby means of a screen printing paste achieves a solder-free connectionwhich is suitable for detecting high temperatures. Screen printingpastes containing silver or silver/platinum are preferably used.

Connections by means of soldering have a restricted field of applicationsince, even at relatively low temperatures, they reach a transitionregion between solid, at their solidus temperature, and liquid, at theliquidus temperature, and thus are no longer suitable for a stableconnection.

In one embodiment, the sensor device has at least two NTC elements whichare connected in parallel with one another.

In another embodiment, the sensor device may have two NTC elements whichare connected in series with one another.

In another embodiment, it is also possible for both NTC elements whichare connected in parallel and NTC elements which are connected in serieswith one another to be arranged on the carrier substrate of the sensordevice.

In one embodiment, two NTC elements which are arranged on differentconductor tracks of the carrier substrate are preferably connected toone another by means of an electrically conductive bridge. In oneembodiment, the bridge comprises the same material as the carriersubstrate of the sensor device.

In one embodiment which has a plurality of NTC elements, for example,the sensor device is also designed to detect a plurality of individualtemperatures or the average temperature of an inhomogeneous temperaturefield.

In one embodiment, the sensor device has at least two NTC elements, eachNTC element being electrically contact-connected by means of at leastone separate conductor track.

In another embodiment, at least two NTC elements of a sensor device, forexample, have at least one common conductor track via which the NTCelements are jointly electrically contact-connected.

A sensor device having two or more NTC elements makes it possible tosimultaneously measure the temperature at different locations with anappropriate design of the conductor tracks. The NTC elements may beelectrically contact-connected in series, in parallel or independentlyof one another via separate conductor tracks for this purpose.

A sensor device like that described above is particularly suitable fordetecting a plurality of temperatures of an inhomogeneous temperaturefield if it is fitted with a plurality of NTC elements. In the case of asensor device having at least two elements, it is possible to detect thetemperatures of an inhomogeneous temperature field.

The sensor device described above is particularly suitable for detectingtemperatures in the range of up to 1000° C. In one preferred embodiment,the sensor device is particularly suitable for detecting temperatures inthe region of 300° C. As a result of the use of a ceramic carriersubstrate and solder-free fastening of the sensor to the substrate, thesensor device is suitable for detecting temperatures up to 1000° C. Inprinciple, the field of application of the sensor device is restrictedonly by the NTC ceramic used since NTC ceramics begin to drift as of acertain temperature.

In one embodiment, the NTC element comprises a ceramic chip which ispreferably in direct electrical contact with at least one of theconductor tracks. In another embodiment, the ceramic chip is inelectrical contact with at least two conductor tracks.

In one embodiment, the ceramic chip of the NTC element has a full-areacontact area on its surfaces. The contact area is preferably applied, inthe form of a metallization made of electrically conductive screenprinting paste, to two opposite surfaces of the NTC element which formconnection regions of the component.

In another embodiment, the metallization made of electrically conductivescreen printing paste is applied in the form of a strip, themetallization preferably being applied in the region of two oppositelateral edges. This makes it possible to set the resistance of theceramic component in a very accurate manner. The metallizationpreferably overlaps the lateral edges with respect to the main surfacesof the NTC element. The metallizations form connection regions of thecomponent, which regions can be used to electrically contact-connect thecomponent.

In another embodiment, the NTC elements are free of metallizations.

NTC elements which have a full-area metallization made of electricallyconductive screen printing paste on both sides are particularly suitablefor serial connection by means of an electrically conductive bridge. Inthe case of a simple structure of the sensor device, in which only oneor more NTC elements which are connected in parallel with one anotherare used, the NTC elements preferably have a metallization which is inthe form of a strip and is made of electrically conductive screenprinting paste in the region of the lateral edges.

In order to make it possible to contact-connect a flat NTC element in aplane, the metallization made of electrically conductive screen printingpaste of the NTC element is preferably in the form of a strip. Inanother embodiment, however, the NTC element may also be free ofmetallizations. In a metallization-free embodiment of the NTC element,the latter is contact-connected, while the screen printing paste isbeing burnt in, by the screen printing paste which has been burnt in. Inthis case, a metallization-free NTC element is arranged on a screenprinting paste, which has not been burnt in and forms the conductortracks, and is burnt in, in a common burning process.

The ceramic carrier substrate is preferably formed from a material withgood thermal conductivity. In the case of a sensor device having one ormore NTC elements which are thermally well coupled, it is possible todetect the average temperature of a temperature field.

The conductor tracks preferably comprise a metal material whose meltingpoint is above the upper application temperature of the sensor device.This ensures sufficiently good temperature stability of the conductortrack.

In one embodiment, the carrier substrate has a thickness which is lessthan the other dimensions. The diameter in the case of a circularcarrier substrate and the length or width in the case of a squarecarrier substrate are preferably greater than the thickness of thecarrier substrate. In one embodiment, the carrier substrate has arectangular base surface. However, the carrier substrate may have anydesired shape.

A carrier substrate having a very small thickness and the use of NTCelements in the form of unpackaged ceramic chips make it possible tokeep the total overall height of the sensor device very low.

In one embodiment, the ceramic carrier substrate can be considered to bean electrical insulator in a wide temperature range, but at least up tothe upper application temperature. This ensures, for example,sufficiently good electrical insulation between a carrier substrate, inwhich conductor tracks are printed on a first side, and the second,opposite side of the carrier substrate.

The sensor device preferably comprises such materials that interactbetween the sensor device and an external time-dependent magnetic fieldcan be considered to be negligible.

In order to manufacture a sensor device, a method is specified, in whichat least one NTC element in the form of a chip on a ceramic carriersubstrate provided is connected to the carrier substrate in amechanically fixed manner by means of an electrically conductive screenprinting paste which can be burnt in.

In a first embodiment of the method for manufacturing a sensor device,an electrically conductive screen printing paste is applied to a ceramiccarrier substrate provided and forms at least two conductor tracks onthe carrier substrate. At least one NTC element is arranged on thecarrier substrate, the NTC element electrically contact-connecting thescreen printing paste which has been printed on via at least twoconnection regions of the NTC element. The connection regions are formedby an electrically conductive screen printing paste which has beenapplied to the NTC element. At least one first connection region of theNTC element is in direct electrical contact with the screen printingpaste. A second connection region may either be in direct or indirectelectrical contact, for example, via a contact bridge and a further NTCelement. In a further method step, the screen printing paste is burntinto the ceramic carrier substrate and the NTC element. As a result ofthe screen printing paste being burnt into the ceramic carrier substrateand the NTC element, the at least one NTC element, the carrier substrateand the screen printing paste which has been burnt in form amechanically stable connection during the burning process.

In another embodiment of a method for manufacturing a sensor device, ascreen printing paste is applied to a ceramic carrier substrate providedand forms at least two conductor tracks on the carrier substrate. Thescreen printing paste is burnt into the ceramic carrier substrate in afirst burning process. At least one NTC element is then arranged on theconductor tracks, the NTC element at least being in electrical contactwith the conductor tracks by means of an applied electrically conductivescreen printing paste after it has been burnt in. The at least one NTCelement may be either in direct or indirect electrical contact with afurther conductor track which has been burnt in. In a second burningprocess, the at least one NTC element and the screen printing pasteapplied to the conductor tracks enter a mechanically stable connectionduring the burning process.

The subject matter described above are explained in more detail usingthe following figures and exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described below should not be interpreted as beingtrue-to-scale. Rather, individual dimensions may be illustrated on anenlarged, reduced or else distorted scale for the purpose of betterillustration. Elements which are the same as one another or whichundertake the same functions are denoted using the same referencesymbols.

FIG. 1 shows a ceramic carrier substrate;

FIG. 2 shows one embodiment of a ceramic component in the form of an NTCelement with metallizations in the form of strips;

FIG. 3 shows a first embodiment of the sensor device having one NTCelement;

FIG. 4 shows another embodiment of the sensor device having two NTCelements which are connected in parallel with one another; and

FIG. 5 shows another embodiment of the sensor device having four NTCelements, two series-connected NTC elements of which are respectivelyconnected in parallel with one another.

The following list of reference symbols may be used in conjunction withthe drawings:

-   -   1 Carrier substrate    -   2 a, 2 b Conductor track    -   3, 3 a, 3 a′, 3 b, 3 b′ NTC element    -   4, 4 a, 4 b Metallization    -   5, 5 a, 5 b Electrically conductive bridge    -   6 Contact region

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 shows a ceramic carrier substrate 1 of a first embodiment of thesensor device. The ceramic carrier substrate 1 preferably has thesmallest dimensions in the region of its thickness. Two conductor tracks2 a, 2 b which were applied to the carrier substrate 1 by means of ascreen printing method are arranged on the ceramic carrier substrate 1.In order to produce the conductor tracks 2 a, 2 b, a screen printingpaste containing silver or silver/platinum, for example, was applied tothe carrier substrate 1 by means of a screen printing method.

The screen printing paste is burnt into the ceramic carrier substrate 1and the ceramic component under the action of very high temperatures.The burning-in process is preferably carried out at temperatures in therange of approximately 700° C. to 900° C.

The screen printing paste which has been burnt in preferably forms theconductor tracks 2 a, 2 b on a top side of the carrier substrate 1. Inthe embodiment illustrated, the conductor tracks 2 a, 2 b have contactregions 6 in the region of one end of the carrier substrate 1. Thecontact regions 6 may be, for example, in the form of separateconnection pads, in the form of widened conductor tracks or in someother form. The contact regions 6 are used to electricallycontact-connect the sensor device. As illustrated in FIG. 1, the contactregions 6 are preferably accessible from a common side of the carriersubstrate 1. However, it is also possible for the contact regions 6 tobe arranged on different sides of the carrier substrate 1 by means ofplated-through holes.

In one possible embodiment, at least one ceramic component, which isillustrated by way of example as an NTC element in FIGS. 2 to 5, isarranged on the carrier substrate 1 and is directly heated with thescreen printing paste. Alternatively, at least one ceramic component mayalso be baked with the conductor tracks 2 a, 2 b in a further, separateburning-in step by means of a screen printing paste.

FIG. 2 shows one embodiment of a ceramic component in the form of an NTCelement 3. The NTC element 3 is preferably in the form of an unpackagedceramic chip (die). In the embodiment illustrated, the NTC element 3 hasmetallizations 4 a, 4 b, which are in the form of strips and can extendover the lateral regions of the NTC element 3 as far as the lateraledges of the latter, on a surface of the NTC element 3 in the region oftwo opposite lateral edges. It is also possible for the metallizations 4a, 4 b in the form of strips to extend beyond the lateral edges as faras the opposite underside of the NTC element 3. A metallization 4 a, 4 bin the form of a strip electrically contact-connects the NTC element 3,for example via two conductor tracks beside one another, after thescreen printing paste has been burnt in.

In another embodiment (not illustrated), the metallization 4 which ismade of an electrically conductive screen printing paste may also beapplied to the entire area of the top side and underside of the NTCelement 3. In this embodiment, a first metallized side of the NTCelement 3 constitutes a first electrical contact for a conductor trackor for a further electrical component after the screen printing pastehas been burnt in. The second electrical contact of the NTC element 3 iselectrically contact-connected via the second metallized side of the NTCelement 3.

FIG. 3 illustrates a first embodiment of the sensor device having oneNTC element 3. In an end region, the NTC element 3 is directly connectedto the conductor tracks 2 a, 2 b of the carrier substrate 1 in anelectrically conductive manner. In the embodiment illustrated, the NTCelement 3 preferably has metallizations, which are in the form of stripsand are made of electrically conductive screen printing paste, in theregion of the lateral edges, which metallizations are not illustrated inFIG. 3 since they are preferably arranged on the underside of the NTCelement 3 in this embodiment. The NTC element 3 is connected to theconductor tracks 2 a, 2 b in a temperature-resistant, mechanically fixedand electrical manner. The NTC element 3 is connected to the conductortracks 2 a, 2 b by means of a screen printing paste. In a burning step,the NTC element 3 is baked with the screen printing paste of theconductor tracks 2 a, 2 b or with a screen printing paste which has beenadditionally applied to the conductor tracks 2 a, 2 b which have alreadybeen burnt in, thus resulting in a high-temperature-resistant,electrically conductive and mechanically stable connection between theconductor tracks 2 a, 2 b of the carrier substrate 1 and the NTC element3.

FIG. 4 shows another embodiment of the sensor device in which two NTCelements 3 a, 3 b are connected in parallel with one another. The twoNTC elements 3 a, 3 b are preferably arranged at a distance from oneanother with respect to the longest extent of the carrier substrate 1.In the embodiment illustrated, the NTC elements 3 a, 3 b are connectedin parallel with one another via the conductor tracks 2 a, 2 b. Anarrangement in which the NTC elements 3 a, 3 b are arranged at adistance from one another on the carrier substrate 1 makes it possible,for example, to detect the average temperature of an inhomogeneoustemperature field. The first NTC element 3 a detects the temperature ina first region of the inhomogeneous temperature field and the second NTCelement 3 b detects the temperature in a second region, the temperaturesof the first and second regions differing from one another. The outputsignal from the two NTC elements 3 a, 3 b produces an electrical signalwhich can be used to determine the average temperature of the twotemperature regions, for example.

In another embodiment (not illustrated), two NTC elements may have acommon forward line and separate return lines, for example. This makesit possible, for example, to determine the different temperatures of aninhomogeneous temperature field separately from one another, preferablyat the same time.

The use of more than two NTC elements, for example, in the case of aparallel circuit, makes it possible to determine a more exact averagetemperature of an inhomogeneous temperature field. In the case of aconnection with separate return lines, it is possible to determine aplurality of temperatures of an inhomogeneous temperature field.

FIG. 5 illustrates another embodiment of the sensor device having fourNTC elements 3 a, 3 a′, 3 b, 3 b′, two series-connected NTC elements 3a, 3 a′ and 3 b, 3 b′ respectively being connected in parallel with oneanother. In the embodiment illustrated, the NTC elements 3 a, 3 a′, 3 b,3 b′ preferably have a full-area metallization made of electricallyconductive screen printing paste on both sides, which metallization isnot illustrated in FIG. 5. In order to contact-connect the NTC elements3 a, 3 a′, 3 b, 3 b′, a first side of the latter is preferably in directcontact with one of the two conductor tracks 2 a, 2 b on the carriersubstrate 1. Two first NTC elements 3 a, 3 a′ are respectivelyelectrically connected to one another via the second side of the NTCelements 3 a, 3 a′, 3 b, 3 b′ by means of an electrically conductivecontact bridge 5 a. The second pair of NTC elements 3 b, 3 b′ islikewise electrically connected by means of an electrically conductivecontact bridge 5 b. The contact bridges 5 a, 5 b preferably comprise thesame ceramic material as the carrier substrate 1. The contact bridges 5a, 5 b have at least one conductor track which is used to electricallyconnect at least two NTC elements 3 a, 3 a′ or 3 b, 3 b′ to one another.

The NTC elements 3 a, 3 a′, 3 b, 3 b′ are preferably mechanically andelectrically connected to the conductor tracks 2 a, 2 b and to theelectrically conductive contact bridges 5 a, 5 b by means ofelectrically conductive screen printing paste applied to both sides. Theconnection of the first sides of the NTC elements 3 a, 3 a′, 3 b, 3 b′to the conductor tracks 2 a, 2 b by means of screen printing paste canalso already be carried out together with the operation of burning thescreen printing paste of the conductor tracks 2 a, 2 b into the ceramiccarrier substrate 1. In one embodiment, it is also possible for theconnection of the second sides of the NTC elements 3 a, 3 a′, 3 b, 3 b′to the respective electrically conductive contact bridges 5 a, 5 b bymeans of electrically conductive screen printing paste to be carried outin a first joint burning step together with the operation of burning inthe conductor tracks 2 a, 2 b.

Although only a restricted number of possible developments of theinvention could be described in the exemplary embodiments, the inventionis not restricted to these developments. In principle, it is possiblefor the sensor device to have a plurality of NTC elements which areconnected via separate conductor tracks, with the result that thedifferent temperatures of an inhomogeneous temperature field can bedetected.

The invention is not restricted to the number of elements illustrated.The description of the subject matters stated here is not restricted tothe individual specific embodiments, but rather the features of theindividual embodiments can be combined with one another as desiredinsofar as technically useful.

What is claimed is:
 1. A sensor device comprising: a ceramic carriersubstrate; at least two conductor tracks arranged on the carriersubstrate; and at least one ceramic component in the form of a chip thatis electrically connected to the conductor tracks, the at least oneceramic component being mechanically connected to the conductor tracksby a screen printing paste that has been burnt in, wherein the screenprinting paste which has been burnt in forms the conductor tracks andwherein the at least one ceramic component is directly connected to theconductor tracks, wherein the at least one ceramic component is free ofmetallization and is directly mechanically connected to the conductortracks such that ceramic material of the ceramic component is in directcontact with a material of the conductor tracks.
 2. The sensor device asclaimed in claim 1, wherein the at least one ceramic component comprisesat least two ceramic components that are arranged on different conductortracks and are electrically connected to one another by an electricallyconductive bridge.
 3. The sensor device as claimed in claim 2, whereinthe electrically conductive bridge comprises the same material as thecarrier substrate.
 4. The sensor device as claimed in claim 1, whereinthe sensor device is designed to detect temperature.
 5. The sensordevice as claimed in claim 4, wherein the sensor device is designed todetect temperatures up to 1000° C.
 6. The sensor device as claimed inclaim 1, further comprising a further ceramic component, wherein the atleast one ceramic component and the further ceramic component are spacedapart in a longitudinal direction of the carrier substrate and are eachelectrically contact-connected by at least one separate conductor track.7. The sensor device as claimed in claim 6, wherein the at least oneceramic component and the further ceramic component are electricallycontact-connected by at least one common conductor track.
 8. The sensordevice as claimed in claim 1, wherein the at least one ceramic componentcomprises a metallization-free ceramic chip.
 9. The sensor device asclaimed in claim 1, wherein the at least one ceramic component comprisesa ceramic component with a full-area metallization made of electricallyconductive screen printing paste on surfaces thereof.
 10. The sensordevice as claimed in claim 1, wherein the at least one ceramic componentcomprises a ceramic component with a metallization that is in the formof a strip.
 11. The sensor device as claimed in claim 10, wherein thestrip is made of electrically conductive screen printing paste and isapplied in a region of two opposite lateral edges.
 12. The sensor deviceas claimed in claim 1, further comprising a further ceramic component,wherein the at least one ceramic component and the further ceramiccomponent are spaced apart in a longitudinal direction of the carriersubstrate and are connected in parallel with one another.
 13. The sensordevice as claimed in claim 1, further comprising a further ceramiccomponent, wherein the at least one ceramic component and the furtherceramic component each comprise at least one group of ceramicsub-components, wherein the at least one group comprises at least twoceramic sub-components that are arranged on different conductor tracksand are electrically connected to one another by an electricallyconductive bridge, and wherein the at least one ceramic component andthe further ceramic component are spaced apart in a longitudinaldirection of the carrier substrate and are connected in parallel withone another.